New results on the strato-mesospheric cooling of the Northern Hemisphere (1969–1978)

Rocketsonde — derived temperature trends within the Northern hemisphere are examined for the stratosphere and lower mesosphere for the period 1969–1978. The rocketsonde records presented here are homogeneous because of are mostly based on the Datasonde system. It appears that stratospheric and lower mesospheric temperature fluctuations in some cases, are about one order of magnitude larger than observed by previous workers. The main features for the temperature trends throughout the decade 1969–1978 are notably: (a) 15 C cooling at 60 km, (b) 5.5 C at 50 km, (c) 5 C at 40 km, (d) 4 C at 30 km, and (e) 3.5 C at 20 km.     

Estimates of the number of sunspot groups: Application to the activity cycle 1960–1970

It was verified that the total number of sunspot groups at certain region on the solar surface for a certain activity cycle can be estimated quite accurately by using the Markov chain approximation method on the total number of spot groups observed on the same region at an earlier activity cycle. Application has been carried out on the observed sunspots on three northern longitude intervals (40–50, 80–90, and 130–140) during the activity cycle 1950–1960 and 1960–1970. The total number of spot groups in these regions for the activity cycle 1960–1970 has been estimated from the observational data of the cycle 1950–1960. A good correlation between the observed and estimated number of spot groups for the activity cycle 1960–1970 has been noted.     

Information limit optimisation techniques applied to recent photometry of Pluto

An algebraic approach originally intended for the heuristic modelling of the maculation effects of chromospherically active stars has been used to model the rotational modulation of Pluto's light. Two dark spots (30.0 ± 0.8 and 16.4 ± 1.4 in radius, at longitudes 3.4 ± 3.2 and 138.0 ± 5.2 degrees, and respective latitudes –35 and –16 ) were found to model the 1982.2 data of Binzel and Mulholland (1983) best. These parameters are in reasonable agreement with the other published models of Pluto's surface for the data, however this model can not be well reconciled with older data sets. A possible solution is dynamic behaviour of the dark features themselves, increasing in radius as perihelion is approached. We stress a minimum in the introduction of ad hoc surface feature hypothesis in this treatment.     

Structure of the martian north polar cap and vernal hood system at L s 61‡–66‡ of the 1995 apparition

The boundary and internal structure of the north polar deposits and polar hood vernal remnant on Mars have been mapped at L _s 61–66 on the hemisphere centered on longitude = 0, using images obtained in Feb–Mar 1995 with the Swedish Vacuum Solar Telescope on La Palma. On red light images, several internal rifts, including the historically well documented Rima Tenuis and Rima Hyperborea, as well as an internal, long absent, annular rift were mapped. The ground cap was asymmetric with a mean boundary at 72 N for = 270, increasing to 77 N at = 90. Images in green light showed the locations of high opacity hood clouds, including an extensive outflow to 67 N at 100. The state of the cap and hood is compared with the findings of previous studies and the historical significance of the annular rift structure is discussed. It is concluded, based on the structure of the deposited laminae, that the north polar climate was nearly, or possibly slightly milder than, normal at the northern hemisphere spring season studied.     

Dependence of the aurora borealis occurrences on the solar-terrestrial parameters

The recent measurements made by satellites of the aurorae in connection with solar phenomena have increased interest in auroral research. In the present investigation, we establish that, for the 20th solar cycle, the occurrence of visual discrete aurorae A, deduced from a complete set of data, is significantly related to the sunspot numbers R _z, the number of flares F (of importance 1) the solar wind streams derived from solar coronal holes H, and the geomagnetic index A _p.By employing the theory of residues it has been found that A correlates significantly well with the above indices. Accuracies of the order of 75–94% were found for geomagnetic latitudes in the range of 54 –63 N.The A-R _zrelationship was investigated in particular for the period 1897–1951. For this period spectrum analysis of A annual values revealed the existence of 3–4 yr and 8–10 yr periodicities of significances 95% and 99%; respectively.Research Associate.     

The limits of possible values of inclination of Mercury's equator

The method of estimation of the limits, containing the equator inclination of a celestial body, had been developed. In this method it is necessary to know the orbital elements and the mass of a celestial body. Another condition is that the axial rotation of a body should be in the resonance with its orbital motion. It has been found that the equator inclinations should have the values between 1 .7 and 2 .6 for Mercury and between 1 .0 and 1 .8 for the Moon. It also has been found that largest harmonics in Mercury's physical libration are the harmonics sin( – 3g), cos( – 3g), sin g and sin 2.     

Imaging Fabry-Pérot observations of [OI] 6300 Å emission in the coma of Halley's comet 1982i

The observation of [OI] 6300 » emission in the coma of Halley's comet 1982i, using the imaging Fabry-Pérot spectrometer, was carried out from Gurushikhar (2439N, 7243E, 1700m altitude), Mt. Abu, India on March 15, 1986 (R = 0.90 AU, = 0.96 AU). The analysis of the interferogram show the absence of the differential velocity of neutral oxygen above 5 km s^–1.     

A laboratory experiment with relevance to the survival of micro-organisms entering a planetary atmosphere

A culture of E.coli was initially subjected to brief exposures to heat for durations of 30–60 s, starting with a temperature of 270 C. A stepwise increase of this temperature from 270 C–750 C and a sequential culturing led to the emergence of a strain of this bacterium with a much higher resistance to flash heating than the original culture possessed. This behaviour would have an important relevance to the survival of micro-organisms upon entering a planetary atmosphere.     

Latitude dependence of auroral frequency in relation to solar — Terrestrial and interplanetary parameters

The auroral frequency of occurrences (A) for the 20th solar cycle and for the geomagnetic latitudes 54–63 N has been investigated in relation to sunspot numbers (R _z), number of flares (F), the solar wind streams derived from the coronal holes (H) and the geomagnetic index (A _p). The relationship between A and the other indices were found to be strongly latitude dependent. At around 57–58 N, a drastic change in this relationship occurs, and an attempt is made qualitatively to evaluate this latitudinal variation.     

Cometary collisions and the dark material on Iapetus

Iapetus (S8) is unique in our solar system in that the albedo of its leading hemisphere is only 0.05 while that of the trailing side is 0.5. Several existing hypotheses are examined and found inadequate. Photometric studies of the dark side are compared to comet nuclei and class D asteroids. It is hypothesized that in the last 10⁶–10⁸ yrs the leading side suffered a high-velocity collision with a cometary body of mass 10¹³–10¹⁵ kg and traveling at a speed of 20 km s^–1. About 5–16% of the excavated material was ejected into space, where the vaporized ices dissipated while the dark carbonaceous/silicate material was reaccreted on the leading side. The collision, although not sufficient to break Iapetus' tidal lock, resulted in a period of oscillation of about 5 yr. Until tidal friction reasserted a lock, the oscillation gave rise to the longitude effect, viz., the observed fact that the dark material covers more than 220 of longitude but only 110 of latitude.     

The first Byurakan Spectral Sky Survey. Stars of later spectral classes. V. The zone +65°⩽δ⩽+69°

We give the fifth list of red stars of the First Byurakan Spectral Sky Survey. The objects are located in the zone 5^h 18^h 30^m and +65 +69. The list contains the data on 18 new objects, one of which is a star of class R. We also give the first determination of the spectral class of 11 variable objects, for four of which we give the spectrograms in the range of wavelengths 4700–6700å.Translated fromAstrofizika, Vol. 37, No. 4, 1994.     

Observations of the GIOTTO target comet P/Grigg-Skjellerup at the Calar Alto Observatory

CCD images of comet P/Grigg-Skjellerup, obtained for astrometric purposes with the 3.5 m telescope at the Calar Alto Observatory/Spain, were used for an analysis of the activity status of the nucleus and for a search of faint coma structures. The nucleus was found essentially inactive beyond 2.7 AU solar distance both inbound and outbound (observations on 12–13 August, 1986, 21–23 October, 1986, 22 August, 1988, 18 October, 1988, 9 and 12 September, 1991 and 3 December, 1991). The coma of the comet was well developed in May and July 1987 with a diameter of at least 190 000 km on 24 May, 1987 and of at least 80 000 km on 24 July 1987. The coma showed a cone of diffuse brightness enhancement in the sunward hemisphere. The orientation of the cone axis changed from the Sun direction in May 1987 towards about North in July 1987, i.e., it was almost perpendicular to the projected Sun-nucleus line on the sky. The cone opening angle became smaller from about 100 in May to about 50 in July 1987. A weak and narrow plasma tail was found in the images of May 1987.     

Mass and orbit estimation of Planet X via a family of comets

The crucial assumption of this paper is, that the observed clustering of aphelion distances of intermediate-period comets in the 70–90 AU range is due to the influence of a tenth planet, called Planet X. We contribute to the search for Planet X a new and extended evaluation of a family of comets assumed to be Planet X's family of comets.By averaging the aphelion distances of comets that belong to a transplutonic family of comets, we get Planet X's semi-major axis a _x = (83.0 ± 5.3) AU. The comets' orbits also yield the upper limit of the planet's orbital eccentricity e _x - 0.019. If this planet played an important part in sending quasi-periodic comet showers to the inner solar system, we can calculate its orbital inclination i _x = 46 .1 ± 3 .6. By distributing all planets' masses into the heliocentric, torus-like zones, in which they were formed, we get the density distribution of the primordial solar nebula. Extrapolating this distribution we find the mass of the planet M _x = (5.1_–2.4 ^+3.6 M _Earth. A few plausible assumptions (e.g. Uranus and Neptune perturbations being caused by Planet X) lead to Planet X's actual location with declination and eccliptic longitude being = 57 ± 17 and = 54 ± 34 , respectively (1989.5 position). In addition, we give Planet X's apparent brightness dependent on its unknown albedo. All those properties and predictions are more or less in agreement with earlier work on Planet X.     

Geology and tectonics of Beta Regio,Guinevere Planitia,Sedna Planitia,and Western Eistla Regio,Venus: Results from Arecibo image data

New radar images (resolution 1.5–2.0 km) obtained from the Arecibo Observatory are used to assess the geology of a portion of the equatorial region of Venus (1 S to 45 N and from 270 eastward to 30). Nine geologic units are mapped on the basis of their radar characteristics and their distribution and correspondences with topography are examined. Plains are the most abundant unit, make up 80%; of the area imaged, and are divided into bright, dark, and mottled. Mottled plains contain abundant lava flows and domes suggesting that volcanism forming plains is a significant process in the equatorial region of Venus. Tesserae are found primarily on Beta Regio and its eastern flank and are interpreted to be locally stratigraphically older units, predating episodes of faulting and plains formation. Isolated regions of tesserae concentrated to the north of Western Eistla Regio are interpreted to predate the formation of plains in this area. The volcanoes Sif Mons, Gula Mons, Sappho, Theia Mons, and Rhea Mons, are found exclusively in highland regions and their deposits are interpreted as contributing only a small percentage to the overall volume of the regional topography. The northern 15 of the image data overlap with Venera 15/16 images making it possible to examine the characteristics of geologic units mapped under various illumination directions and incidence angles. Surface panoramas and geochemical data obtained from Venera landers provide ground truth for map units, evidence that plains are made up of basaltic lava flows, and that linear deformation zones contain abundant blocks and cobbles. On the basis of spatial and temporal relationships between geologic units, the highlands of Beta Regio and Western Eistla Regio are interpreted to have formed in association with areas of mantle upwelling which uplift plains, cause rifting, and in the case of Beta Regio, disrupt a large region of tessera. Zones of linear belt deformation in Beta Regio and Western Eistla Regio are interpreted to be extensional and indicate that at least limited extension has occurred in both regions. The images reveal for the first time that southern Devana Chasma is a region of overlapping rift valleys separated by a distance of 600 km. Linear deformation zones in Guinevere Planitia, separating Beta Regio and Eistla Regio, converge at a region of ovoids forming a discontinuous zone of disruption and completes an equatorial encompassing network of highlands and tectonic features. The similarity between ovoids and coronae suggests a mechanism of formation associated with hotspots or mantle plumes. Analysis of the distribution and density of impact craters suggests a surface age for this part of the planet similar to or slightly less than that determined for the northern high latitudes from Venera 15/16 data (0.3 to 1.5 by) and comparable to that calculated for the southern hemisphere.     

Dynamics of Blinkers

The relative Doppler and non-thermal velocities of quiet-Sun and active-region blinkers identified in Ov with CDS are calculated. Relative velocities for the corresponding chromospheric plasma below are also determined using the Hei line. Ov blinkers and the chromosphere directly below, have a preference to be more red-shifted than the normal transition region and chromospheric plasma. The ranges of these enhanced velocities, however, are no larger than the typical spread of Doppler velocities in these regions. The anticipated ranges of Doppler velocities of blinkers are 10–15 km s^–1 in the quiet Sun (10–20 km s^–1 in active regions) for Hei and 25–30 km s^–1 in the quiet Sun (20–40 km s^–1 in active regions) for Ov. Blinkers and the chromosphere below also have preferentially larger non-thermal velocities than the typical background chromosphere and transition region. Again the increase in magnitude of these non-thermal velocities is no greater than the typical ranges of non-thermal velocities. The ranges of non-thermal velocities of blinkers in both the quiet Sun and active regions are estimated to be 15–25 km s^–1 in Hei and 30–45 km s^–1 in Ov. There are more blinkers with larger Doppler and non-thermal velocities than would be expected in the whole of the chromosphere and transition region. The recently suggested mechanisms for blinkers are revisited and discussed further in light of the new results.     

Formation of Planetesimals in the Trans-Neptunian Region of the Protoplanetary Disk

We consider the formation of cometlike and larger bodies in the trans-Neptunian region of the protoplanetary gas–dust disk. Once the particles have reached 1–10 cm in size through mutual collisions, they compact and concentrate toward the midplane of the disk to form a dust subdisk there. We show that after the subdisk has reached a critical density, its inner, equatorial layer that, in contrast to the two subsurface layers, contains no shear turbulence can be gravitationally unstable. The layer breaks up into 10¹²-cm clumps whose small fragments (10⁹ cm) can rapidly contract to form bodies 10 km in size. We consider the sunward drift of dust particles at a velocity that decreases with decreasing radial distance as the mechanism of radial contraction and compaction of the layer that contributes to its gravitational instability and the formation of larger (100 km) planetesimals. Given all of the above processes, it takes 10⁶ yr for planetesimals to form, which is an order of magnitude shorter than the lifetime of the gas–dust protoplanetary disk. We discuss peculiarities of the structure of planetesimals.     

Evolution of the spectral fine structure of Jupiter's decametric S-storms

High-resolution spectra of Jupiter's decametric S-storms are studied with an acousto-optical radio spectrograph operating over the frequency range 20–30 MHz. In 1985–1989 20 S-storms were recorded in the Io-B region. There is only a slight average zoning effect of certain types of fine structure in the Io-B region, with sporadic S-bursts occurring most often in the early CML values, and S-trains in the late values. Emissions of type N and its variants occur at lower values of the Io phase than S-emissions and their variants. There is no exact storm-to-storm correspondence, nor any Io-B-centered zones in which the various types of fine structure could be accurately placed. Every storm is different and has a signature of its own. An important exception is formed by the wide-range quasi-periodic FDS-S storms that occur at the edge of the Io-B region with Io phase values greater than 80 . These are outstanding storms in which the individual bursts may extend across the full spectral width of 20–30 MHz and be repeated in rapid succession at quasi-periodic rates of 20–40 s^–1. It is suggested that these be referred to as type Q storms. It is estimated that only 10% of the S-burst types are recorded so far.     

On arch-filament systems in spotgroups

Systems of arch-shaped filaments (AFS) occurring in the interspot region of young bipolar groups are studied. Their main characteristics are: Average length: 30000km, average width 20000km, width of individual filaments 1000–3000 km, height of arches 4–15000 km. A typical lifetime of the filaments 30 min; appreciable changes of the system occur within several hours; the lifetime of a system is about three days. - The arch-filament systems bridge the neutral line and connect the regions of the innermost spots of opposite polarity. Material moves along the filaments (v 25–50 km/sec) following the direction of the magnetic field, and sometimes arches are observed rising at a rate of 20 km/sec. They are very dark on the inner disk and appear either in emission or in absorption close to the solar limb. - The occurrence of bright points (moustaches) is found to be closely associated with AFS in young spotgroups. - The possible nature of AFS and their relation to other types of filamentary structures is discussed.     

Asteroids approaching the Earth from directions around the Sun

We have estimated close asteroid encounters with the Earth by numerical integrations of a system with the Sun, 9 planets, and 188 near-earth-asteroids during the period 1994–4600. Asteroids approach the Earth from directions within 30 around the Sun in more than 20% of encounters with the closest distance less than 0.01 AU. Since ground-based observations cannot detect these objects, we should develop space-borne and/or lunar observatories in a short time to allow enough warning time before a catastrophic collision.     

The dynamics of the ring nebula surrounding the LBV candidate He 3-519

High spatial and spectral resolution observations of the ring nebula surrounding the LBV candidate He 3-519 are presented. The data were obtained at the AAT with the UCL echelle spectrograph and cover the H and [N II] emission lines for two slit positions. The nebular motions are clearly resolved and have a total velocity spread of -40 to +100 km s^–1. The shell shows some deviations from spherical symmetry but overall is expanding at 61 km s^–1 and has an ionized mass of 2 M. The nebular parameters are found to be similar to those of the AG Car nebula, suggesting that it resulted from a bulk ejection of material 2 × 10⁴ yr ago.